Servo amplifier



Jan. 9, 1962 H. w. MATHERS 3,016,485

SERVO AMPLIFIER Original Filed Jan. 16, 1956 2 Sheets-Sheet 1 SINGLEFERROMAGNETIC CORE F D 1 I NE CONTROL OUT b a SIGNAL 10 n *2 3 4 v I 6OORE BECOMES SATURATED AT 1 AND CURRENT IS DE- TERMINED BY RL AND EMAGNETIZING CURRENT I\ IL INDUCED VOLTAGE Ec.= N5}; N$

FIG. 3

Jan. 9, 1962 H. w. MATHERS 3,016,485

SERVO AMPLIFIER Original Filed Jan. 16, 1956 2 Sheets-Sheet 2 FIG; 4A

LOAD F |G.5

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ESPHASEA A Patented Jan. 9, 1%62 ice This application is a continuationof copending application, Serial Number 559,262, now abandoned, filedJanuary 16, 1956, and entitled Servo Amplifier.

This invention relates to an improved transistor controlledmagnetic'servo amplifier. 1 More particularly, the novel transistorcontrolled am"- plifier herein disclosed and claimed includes ac'o're offerromagnetic material having a power winding, a bias winding and 'acontrol winding elec'tromagnetically coupled to the core. The ratiobetween the turns of the bias and control windings is such that theampere turns of the control winding can be controlled to efiectivelycancel a substantial portion of the biaswindingampe're turnsand thuspreclude the core-from arriving at a lower point on its hysteresiscurve. Assuming the control windings have been eifective in oiisettingthe bias windings, then subsequent thereto, the core will reachsaturation upon the supplying of far less voltage to the power windings.

One object of the present invention is the provision of a transistorcontrolled magnetic servo amplifier wherein the requirement of an AC. orDC. power source for the transistor circuit is eliminated.

A further object of the present invention is an improved transistorcontrolled magnetic servo amplifier wherein the physical size and theelectrical power consumption are respectively reduced.

A still further object of the present invention is an improvedtransistor controlled magnetic servo amplifier that is highly stable andhighly reliable in operation and has a long life.

Other objects of the invention will be pointed out in the followingdescriptions and claims and illustrated in the accompanying drawings,which disclose, by way of example, the principle of the invention andthe best mode, which has been contemplated, of applying that principle.

In the drawings:

FIG. 1 discloses a first circuit that may be employed to practiceapplicantsinvention;

FIG. 2 discloses an idealized BH curve or hysteresis loop for theferromagnetic cores, respectively, employed in the circuits of FIGS. 1,4A and 413;

FIG. 3 discloses idealized voltage and current waveforms utilizedhereinafter in disclosing a typical mode of operation of the circuit ofFIG. 1;

FIGS. 4A and 413, respectively, disclose transistor controlled magneticservo amplifier circuits with phase reversible output, that may beemployed to practice applicants invention;

FIG. 5 discloses how the power windings of the circuit of FIG. 2 aredivided in arriving at the alternative embodiments of the inventiondisclosed in FIGS. 4A and 4B, respectively; and

FIG. 6 discloses idealized current and voltage waveforms utilizedhereinafter in disclosing a typical mode of; 1 operation of the circuitsof FIGS. 4A and 4B.

Referring to FIG. 1, it will be seen that between leads 10 and 11,across which an input E is impressed, there are two parallel branches,respectively consisting, of the serial connection, in the order recited,of a power winding 2 as diode 58 will oifer very little opposition tocurrent flowing from lead 11 to lead 10. An output is taken from acrossresistor R Still referring to FIG. 1, it will be seen that the controlwinding of the ferromagnetic core, namely, Winding N has one endconnected via lead 14, to the base electrode of transistor TRl. Theother end of control winding N is connected through diodes S to thecollector electrode of transistor TRl. Lead 13 is connected to theemitter electrode of transistor TR1. (The connections shown are for anNPN transistor.) It will be appreciated that diodes S offers very littleopposition to a flow of current from lead '14 to the collector electrodeof transistor TRl. In other words, the cathode of diode S is connectedto the collector of transistor TRI. In the operation of the circuit ofFIG. 1, leads 13 and 14 will have impressed thereon a control signalvoltage E of proper magnitude and time relation with respect to thevoltage E so as to control the rendition of a substantial output voltageacross resistor R at predetermined times.

The operation of the transistor controlled magnetic servo amplifier ofFIG. 1 will now be explained. Referring to FIG. 2, an idealized squaretype hysteresis loop similar to the actual hysteresis loop of the coreis disclosed. For purposes of explanation, assume that the core flux isat point A of the curve of FIG. 2 at time t of FIG. 3. The ferromagneticcore area and the number of turns of the power winding N are such thatthe voltage time integral between times t and t (FIG. 3) will cause thecore flux to just reach point B (FIG. 2) or saturation and return toresidual point C (FIG. 2) at time t Diode S will prevent the flow ofcurrent in the power winding N during time t to of FIG. 3. However,diode S will permit current to flow in bias winding N during this time,namely, t and t The flow of current in bias winding N tends to cause thecore flux to cycle the hysteresis loop of FIG. 2 from point C towardpoint D. By properly adjusting the ohmic value of resistor R the coreflux can be set to return to any level between points C and A at time 1of FIG. 3. Assume that the ohmic value of resistor R is of suchmagnitude that the core flux returns to point A of FIG. 2, at time tThen the core flux, in the absence of a control signal E will cycle thehysteresis loop A, B, C, D, A during each time interval corresponding totime interval, T to t The core magnetizing current required to traversethe hysteresis loop A, B, C, D, .A is not more than a few milliamperes.Further, it is to be appreciated that core flux changes induce an ACvoltage E (FIG. 3), in control Winding N of FIG. 1.

If a control signal voltage E of the proper phase relationship withrespect to E is applied between the emitter and base electrodes oftransistor TR1 during a negative half cycle of E the transistor willbecome a low impedance path and the control winding voltage E will causea control current to How. The control winding ampere turns N 1 subtractfrom the bias winding ampere turns, N I thus preventing the core fluxfrom reaching point Aat the end of a negative half cycle of Now assumethat a suitable control signal voltage, for example, E of FIG. 3 wasapplied, during time t to r to leads 13 and 14 of FIG. 1. Further,assume that the ampere turns of the control winding N during time to tare approximately equal to one half of the bias winding (N ampere turnsN I Then it will be seen that the core flux will be at point B of FIG. 2at time t .of FIG. 3. I

Now under the preceding assumptions, it will be seen that theferromagnetic core requires (since it is starting from point E) onlyapproximately one half of the voltage time integral from timest to t ofFIG. 3 to change the core flux from point E to point B, or saturation.Thus the core will become saturated at time and the remaining portion ofE will appear across the lead resistor R The load current I is shown inFIG. 3, in the absence of a control signal E for times t to t and in thepresence of a control signal for times t to t It will be apparent thatany control signal (A.C., D.C. or pulse) applied during a negative halfcycle of E can'be used to control the output of this circuit.

Athough the operation described above assumed that the components hadideal characteristics, an actual embodiment employing readily availablecomponents was found to have characteristics closely approaching thoseset forth above. Further, it will be apparent that by controlling thecontrol winding current a variation in the duration and magnitude of theoutput signal and hence the output power is obtainable.

It will now be apparent that the circuit of FIG. 1 requires no A.C. orD.C., source in the control circuit to obtain the necessary controlcurrent.

It will also be apparent that the magnetic amplifier circuit shown inFIG. 1 can be used to form a number of useful circuits. One such circuitsuitable for servo amplifier applications is shown in FIG. 4A. Othercornbinations of the circuit of FIG. 1 could be used for full wave AC.or full wave rectified D.C. output.

The operation of the circuit of FIG. 4A is as follows: The power windingN ofFIG. 1 is divided into two equal portions, Npi and N as shown inFIG. 5. Two ferromagnetic cores with divided power windings are thenconnec'te to a common load such that each ferromagnetic core willdeliver an output to the load during alternate half cycles of E In thecircuit of FIG, 4A, windings on ferromagnetic coie 1 have odd numericalub= scripts and windings on ferromagnetic core 2 have even numericalsubscripts. Control is achieved when a power winding is not conducting(FIGS. 1 and 3) Therefore both cores of the circuit of HG. 4A canbecontrolled by a singletransistor. Resistor R reduces the effects ofthe transistor Ic temperature characteristics.

Reference is made to the typical outputs of the circuit of FIG. 4A asshown in FIG. 6. For E of phase A (in phase with E the control causesferromagnetic core 1 to deliver an output, but has no effect onferromagnetic core 2. For E of phase B (180 with respect to phase Eferromagnetic core 2 gives an output but ferromagnetic core 1 isnoteifected. The outputs I shown in FIG. 6 have large fundamentalcomponents that are of a 0 or 180 phase with respect to E Therefore thecircuit has a phase reversible type output that can be used for servomotor applications.

In a circuit such as FIG. 4A, the bias windings are often adjusted sothat both cores deliver a small output when the magnitude of controlsignal B is equal to zero. A control signal E will then increase'theoutput of one core but will not reduce the output of the other core.Feedback windings N and N connected as shown in FIG. 4B use the loadcurrent of one core to aid the bias winding current in reducing theoutput of the other core. Feedback windings N and N reduce the requiredcontrol signal and improve the control characteristic.

While the invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein withoutdeparting from the spirit and scope of the in:vention.

I claim:

1. An amplifier circuit consisting in combination of: a firstferromagnetic core having a substantially rectangular hysteresischaracteristic; a second ferromagnetic core having a substantiallyrectangular hysteresis characteristic; a first power input terminal anda second power input'terminal; a source of alternating potentialconnected across saidrfirst and second powerinput terminals; a firstdiode 5 having an anode and a cathode; a second diode having ananode anda cathode; a third diode having an anode and a cathode; a fourth diodehaving an anode anda cathode; a fifth diode having an anode and acathode; a sixth diode having an anode and a cathode; a seventh diodehaving an anode and a cathode; an eighth diode having an anode and acathod-e; a transistor having an emitter electrode, a base electrode anda collector electrode; a first series circuit directly connected betweensaid first power input terminal and said anode of said second diode;said first series circuit consisting in seriatim of a first powerwinding electromagnetically coupled to said first ferromagnetic core ina first sense of electromagnetization and a first feedback windingelectromagnetically coupled to said second ferro magnetic core inasecond sense of electromagnetization, opposite to said first sense ofelectromagnetization; a second series circuit directly connected betweensaid first power input terminal and said cathode of said first diode,said second series circuit consisting in seriatim of a second powerwinding electromagnetically coupled to said second ferromagnetic core insaid second sense of electromag netization and a second feedback windingelectromagnetically coupled to'said first ferromagnetic core in saidfirst sense of clectromagnetization; a first output terminal; a secondoutput terminal; a direct connection between said anode of said firstdiode, said anode of said third diode, and said first output terminal; adirect connection between said cathode of said second diode, saidcathode of said fourth diode, and said second output terminal; a

third power winding electromagnetically coupled to said firstferromagnetic core in said first sense of electromagnetization, saidthird power winding being directly connected between said cathode ofsaid third diode and said second power input terminal; a fourth powerwinding electromagnetically coupled to said second ferromagnetic core insaid second sense of electromagnetization, said fourth power windingbeing directly connected between said anode of said fourth diode andsaid second power input terminal; a first bias windingelectromagnetically coupled to said first ferromagnetic core in saidfirst sense of electromagnetization, said first bias'winding beingdirectly connected between said cathode of said fifth diode and saidfirst power input terminal; a second bias winding electromagneticallycoupled to said second ferromagnetic core in said second sense ofeleotromagnetization, said second bias winding being directly connectedbetween said anode of said sixth diode and said first power inputterminal; a first resistor connected between said anode of said fifthdiode and said cathode of said sixth diode, said first resistor havingan adjustable tap directly connected to said second power inputterminal; a first control winding electromagnetically coupled to saidfirst ferromagnetic core in said first sense of electromagnetization,said first control winding being directly connected between said anodeof said seventh diode and said base electrode of said transistor; asecond control winding electromagnetically coupled to said secondferromagnetic core in said second sense of electromagnetization, saidsecond control winding being directly connected between said anode ofsaid eighth diode and said base electrode of said transistor;'a directconnection between said cathode of said seventh diode, said cathode ofsaid eighth diode, and said collector electrode of said transistor; asecond resistor connected between said collector and said baseelectrodes of said transistor; a transformer having a primary and asecond winding, said primary winding being directly connected acrosssaid emitter and said base electrodes of said transistor; a source ofcontrol potential directly connected across said secondary winding ofsaid transformer, whereby a reversible output is obtained across saidoutput terminals under control of said control potential.

2. A transistor controlled magnetic servo amplifier netic core having asubstantially rectangular hysteresis characteristic; a first power inputterminal and a second power input terminal; a source of alternatingpotential connected across said first and second power input terminals;a first diode having an anode and a cathode; a second diode having ananode and a cathode; a third diode having an anode and a cathode; afourth diode having an anode and a cathode; a fifth diode having ananode and a cathode; a sixth diode having an anode and a cathode; aseventh diode having an anode and a cathode; an eighth diode having ananode and a cathode; a transistor having an emitter electrode, a baseelectrode and a collector electrode; a first series circuit directlyconnected between said first power input terminal and said anode of saidsecond diode, said first series circuit consisting in seriatim of afirst power winding electromagnetically coupled to said firstferromagnetic core in a'first sense of electromagnetization; a secondseries circuit directly connected between said first power inputterminal and said cathode of said first diode, said second seriescircuit consisting in seriatim of a second power windingelectromagnetically coupled to said second ferromagnetic core in saidsecond sense of electromagnetization; a first output terminal; a secondoutput terminal; a direct connection between said anode of said firstdiode, said anode of said third diode, and said first output terminal; adirect connection between said cathode of said second diode, saidcathode of said fourth diode, and said second output terminal; a thirdpower winding electromagnetically coupled to said first ferromagneticcore in said first sense of electromagnetization, said third powerwinding being directly connected between said cathode of said thirddiode and said second power input terminal; a fourth power windingelectromagnetically coupled to said second ferromagnetic core in saidsecond sense of electromagnetization, said fourth power winding beingdirectly connected between said anode of said fourth diode and saidsecond power input terminal; a first bias winding electromagneticallycoupled to said first ferromagnetic core in said first sense ofelectromagne-tization, said first bias winding being directly connectedbetween said cathode of said fifth diode and said first power inputterminal; a second bias winding electromagneticaliy coupled to saidsecond ferromagnetic core in said second sense of electromagnetization,said second bias winding being directly connected between said anode ofsaid sixth diode and said first power input terminal; a first resistorconnected between said anode of said fifth diode and said cathode ofsaid sixth diode, said first resistor having an adjustable tap directlyconnected to said second power input terminal; a first control windingelectromagnetically coupled to said first ferromagnetic core in saidfirst sense of electromagnetization, said first control winding beingdirectly connected between said anode of said seventh diode and saidbase electrode of said transistor; a second control windingelectromagnetically coupled to said second ferromagnetic core in saidsecond sense of electromagnetization, said second control winding beingdirectly connected between said anode of said eighth diode and said baseelectrode of said transistor; a direct connection between said cathodeof said seventh diode, said cathode of said eighth diode, and saidcollector electrode of said transistor, a second resistor connectedbetween said collector and said base electrodes ofsaid transistor; atransformer having a primary and a second winding, said primary windingbeing directly connected across said emitter and said base electrodes ofsaid transistor; a source of control potential directly connected acrosssaid secondary winding of said transformer, whereby a reversible outputis obtained across said output terminals under control of said controlpotential.

3. A transistor controlled magnetic servo amplifier adapted to render aphase reversible output, said transistor controlled magnetic servoamplifier consisting in combination of: a first ferromagnetic corehaving a' substantially rectangular hysteresis characteristic; a secondferromagnetic core having a substantially rectangular hysteresischaracteristic; a first power input terminal and a second power inputterminal; a source of alternating potential connected across said firstand second power input terminals; a first diode having an anode and acathode; a second diode having an anode and a cathode; a third diodehaving an anode and a cathode; a fourth diode having an anode and acathode; a fifth diode having an anode and a cathode; a sixth diodehaving an anode and a cathode; a

' seventh diode having an anode and a cathode; an eighth diode having ananode and a cathode; a transistor having an emitter electrode; a baseelectrode and a collector electrode; a first series circuit directlyconnected between said first power input terminal and said anode of saidsecond diode, said first series circuit consisting in seriatim of afirst power winding electromagnetically coupled to said firstferromagnetic core in a first sense of electromagnetization and a firstfeedback winding electromagnetically coupled to said secondferromagnetic core in a second sense of electromagnetization, oppositeto said first sense of electromagnetization; a second series circuitdirectly connected between said first power input terminal and saidcathode of said first diode, said second series circuit consis-ting inseriatim of a second power winding electromagnetically coupled to saidsecond ferromagnetic core in said second sense of electromagnetizationand a second feedback winding electrornagnetically coupled to said firstferromagnetic core in said first sense of electromagnetization; a firstoutput terminal; a second output terminal; a direct connection betweensaid anode of said first diode, said anode of said third diode, and saidfirst output terminal; a direct connection between said cathode of saidsecond diode, said cathode of said fourth diode, and said second outputterminal; a third power winding electromagnetically coupled to saidfirst ferromagnetic core in said first sense of electromagnetization,said third power winding being directly connected between said cathodeof said third diode and said second power input terminal; a fourth powerwinding electromagnetically coupled to said second ferromagnetic core insaid sense of electromagnetization, said fourth power winding beingdirectly connected between said anode of said fourth diode and saidsecond power input terminal; a first bias winding electromagneticallycoupled to said first ferromagnetic core in said first sense ofelectromagnetization, said first bias winding being directly connectedbetween said cathode of said fifth diode and said first power inputterminal; a second bias winding electromagnetically coupled to saidsecond ferromagnetic core in said second sense of electromagnetization,said second bias winding being directly connected between said anode ofsaid sixth diode and said first power input terminal; a first resistorconnected between said anode of said fifth diode and said cathode ofsaid sixth diode, said first resistor having an adjustable tap directlyconnected to said second power input terminal; a first control windingelectromagnetically coupled to said first ferromagnetic core in saidfirst sense of electromagnetization, said first control winding beingdirectly conneoted between said anode of said seventh diode and saidbase electrode of said transistor; a second control windingelectromagnetically coupled to said second ferromagnetic core in saidsecond sense of electromagnetization, said second control winding beingdirectly connected between said anode of said eighth diode and said baseelectrode of said transistor; a direct connection between said cathodeof said seventh diode, said cathode of said eighth diode, and saidcollector electrode of said transistor; a second resistor connectedbetween said collector and said base electrodes of said transistor; atransformer having a primary and a second winding, said primary windingbeing directly connected across said emitter and said base electrodes ofsaid transistor; a source of control potential di rectly connectedacross said secondary winding of said transformer, whereby a reversibleoutput is obtained across said output terminals under control of saidcontrol potential.

No references cited.

